You get your genotype from your parents. Depending on what your parents have genetic wise will be your possible genotype match. So lets say your Mom is heterozygous Rr, this is for black hair and your dad is blond which is rr. Blond being the recessive type you have 2 possible types of hair being black and blond. There is a 50% of having black Hair and 50% of having blond hair in this situation.